Read about this serious threat to your smartphone, involving voice commands by a nearby computer.

You may think watching videos on your phone is a harmless way to pass time, but watch out: Newly discovered voice commands could be hidden inside those videos to hack your smartphone through voice recognition.

To an untrained ear, the message may seem like noise, but for smartphone voice assistants, the message is clear.

“[The command could be in] some popular YouTube video that has this strange noise in the background that a human being would just dismiss as an oddity, but that at the same time that noise could be controlling a cellphone that just happens to be located next to a computer,” said Micah Sherr, an associate professor in Georgetown University’s Department of Computer Science.

Sherr, along with other researchers at Georgetown and University of California, Berkeley discovered the vulnerability.